Loss of insulin producing beta cells is a major problem of T1D and neither therapies that target this process nor simple measures/biomarkers that quantify it are currently available in humans. We recently discovered thioredoxin-interacting protein (TXNIP) as an attractive target in this regard, since genetic or pharmacological TXNIP downregulation with verapamil reduced beta cell apoptosis, increased pancreatic beta cell mass, and protected against and even reversed diabetes in mice. Now our, randomized, double-blind, placebo-controlled trial revealed that oral verapamil added for 12 months to a standard insulin regimen in adult subjects with recent onset T1D improved mixed meal-stimulated C-peptide area under the curve as a measure of endogenous beta cell function. While these findings have the advantage that they can be readily implemented into the clinic, they also underline the need for more specific tools to inhibit TXNIP. In fact, a novel, non-toxic, small molecule TXNIP inhibitor has now shown great promise in mouse models and human islets exposed to T1D-associated inflammatory cytokines. We further discovered that a specific TXNIP-induced microRNA is not only the most highly enriched microRNA in human beta cells, but is also released from dying beta cells, detectable in mouse and human serum, increased in T1D, and inversely correlated with remaining beta cell function. We therefore hypothesize that TXNIP inhibition provides a novel treatment strategy for T1D and that this serum microRNA represents an early diagnostic biomarker for T1D-associated beta cell loss in humans. To test this hypothesis we propose the following Specific Aims: #1: Study the effects of TXNIP inhibition as a novel treatment strategy for T1D including (i) test the effects of oral inhibitor administration on humanized mice using xenotransplantation of human islets into immunedeficient NRG-RIP-DTR mice to assess how TXNIP inhibition affects human islets in vivo in the context of diabetes and (ii) determine how the inhibitor functions and affects islet biology at a molecular level by elucidating the changes in gene expression and pathways involved using our reagents pertaining to TXNIP regulation and RNA sequencing of treated human islets. #2: Assess serum microRNA changes as an early diagnostic biomarker for T1D-associated beta cell loss. We will further explore our serum microRNA as a biomarker for T1D-associated beta cell loss during (i) disease progression as well as (ii) in response to verapamil-induced protection of beta cell function, taking advantage of our unique resource of pre-collected T1D serum samples from our clinical verapamil trial and (iii) will investigate the possibility that increased serum microRNA levels might predate the onset of T1D and could be used as an early marker for disease in at-risk subjects. Consistent with the goals of this HINR-CBDS RFA, the proposed studies will help develop a novel early T1D treatment strategy and a clinical diagnostic tool for the detection and staging of recently-diagnosed individuals with T1D.